Carl Sagan, astronomer
WHEN
1977 onwards
ENDEAVOUR
Launching the first spacecraft to visit the outer planets of the Solar System.
HARDSHIPS & DANGERS
The Voyager spacecraft faced a multitude of technical risks, as well as braving cosmic radiation and space debris.
LEGACY
The two Voyager spacecraft made astonishing discoveriesaboutJupiter, Saturn, Uranus and Neptune. Voyager 1 is now the farthest away human-made object in space at roughly 20 billion km (12.5 billion miles). It has left our Solar System and is in interstellar space.
An artist’s impression of Voyager 1 entering interstellar space.
The Apollo 11 moon landing in 1969 captured the public imagination unlike any other space mission in history. However, in terms of furthering our understanding of the Solar System and the galaxy beyond, NASA’s Voyager mission is arguably of far greater significance. Almost 40 years since their launch, the twin Voyager 1 and 2 spacecraft are now further away from Earth than anything else mankind has ever constructed, some 20 billion km in the case of Voyager 1. Their primary mission was to fly by Jupiter and Saturn and send back data that would ultimately re-write astronomy text-books. However, the mission has become far more successful than could ever have been imagined at the outset.
Interplanetary slingshot
In 1964, Gary Flandro was working at the NASA Jet Propulsion Laboratory and was given the task of examining ways to explore the outer planets. During the course of his study, he discovered a rare alignment of the outer planets that occurred just once every 175 years. This alignment would allow spacecraft to travel from planet to planet, utilizing their gravitational pull and thus accelerating them out into deep space. Instead of taking forty years, the mission duration could be reduced to less than ten.
Voyager 2 was the first spacecraft to be launched from Cape Canaveral in August 1977, followed by Voyager 1 a few weeks later. On board were an array of instruments including video cameras, magnetometers, plasma detectors, infrared and ultraviolet sensors, and cosmic-ray and charged-particle sensors. Most intriguingly though, gold records were also attached to the side of each spacecraft. Each disk contains scenes, greetings, music and sounds of the Earth. These include 115 images and a variety of natural sounds such as those made by whales, birds and other animals. There are recordings of the wind, thunder and surf crashing on a beach. There are greetings in fifty-five different languages and a selection of music ranging from Mozart to Chuck Berry’s Johnny B Good. One day, it is hoped that this record of humanity and Earth will be found by some distant intelligent life-form. In reality though, it would be comparatively less noticeable in the vastness of space than a single grain of sand on an ocean beach. Nevertheless, it was a clever public relations move and ensured global media coverage of the mission.
Both spacecraft have a Golden Record attached to them.
The super-sized storm
On March 3, 1979 Voyager 1 reached Jupiter, flying by the giant gas planet some 200,000 km above the planet’s cloud tops. Voyager 2 passed by a few months later. Although Jupiter had been studied for centuries from Earth – most famously by the Italian astronomer Galileo – scientists were surprised by many of the Voyager findings. Voyager’s cameras recorded videos of the Great Red Spot, which is 3.5 times larger than Earth and which was found to be a complex storm that moved across the planet in a counterclockwise direction and has been raging for centuries.
The most unexpected discovery at Jupiter was on the innermost of its four large moons, Io. Here, for the first time, active volcanoes were seen on a body in the Solar System, other than on Earth. The plumes of which reached 240 km (150 miles up), high enough to hit passing satellites. These volcanoes are thought to be caused by the gravitational tug of war between Jupiter and two of the planet’s other nearby satellites, Europa and Ganymede. This discovery fundamentally changed our opinion and increased our interest in the moons orbiting other planets. Voyager 2 also revealed fascinating details about Europa. This moon’s surface is a thick crust of ice, laced with vivid lines and streaks that may indicate that minerals from below the surface have penetrated the ice. Europa’s conditions could possibly support alien life, albeit in the form of single-celled microorganisms.
An artist’s impression of the Voyager spacecraft – as well as those from the earlier Pioneer mission – at the edges of our Solar System.
Unlocking the secret of the rings
Saturn’s rings. The colour variations indicate different chemical compositions.
The orbit around Jupiter accelerated both spacecraft towards their next destination, Saturn. In November 1980, and just 7.5 km (12 miles) off course, Voyager 1 sent back beautiful close-ups of Saturn’s rings, revealing incredible structures within them. The rings are composed of billions of particles, ranging from dust-size to much larger rocks the size of houses. One of the most memorable images of the entire Voyager mission was that of the spinning rings, backlit by the sun like giant spokes on a wheel. Voyager 1 then flew within 1,500 km (2,500 miles) of Titan, Saturn’s largest moon. It is one of only three moons known to have an atmosphere, made up mainly of nitrogen as well as methane. As a result, the photochemistry is thought to be similar to that of an early Earth, before life took hold.
After this close up view of Titan, Voyager 1 then moved out of the plane of the Solar System towards interstellar space, its main mission complete.
The world in a twist
By 1986, Voyager 2 was now approaching Uranus. It found that the planet spins like the other planets but is tipped on its side. Scientists believe this was caused by a collision with a planet-sized body early in the history of the Solar System. As a consequence, its magnetic field is twisted by Uranus’ unusual rotation into a long corkscrew shape behind the planet. Uranus was also found to be the coldest planet in the Solar System. It is not the furthest planet from the sun but it has no internal heat source.
Voyager 2 also discovered ten additional moons to add to the five that were already known. The most interesting of Uranus’ moons was Miranda, one of the most bizarre objects in the Solar System with 19-km (12-mile) deep canyons and giant escarpments. Its surface is an assortment of terrains and looks as though it has been glued together. Not surprisingly therefore, astronomers once believed that Miranda was smashed to pieces and re-assembled under its own gravitational pull. This could explain its bizarre configuration but the actual reason is still something of a mystery.
More mind-bending discoveries
Travelling at 64,000 km/h (40,000 mph), Voyager 2 made its rendezvous with Neptune, the last of the outer planets, in August 1989. It was just 35 km (22 miles) off its charted course and 1 second off its projected flyby time. The encounter revealed a storm the size of Earth with the fastest winds ever measured in the Solar System of nearly 1,600 km/h (1,000 mph). This astonished NASA scientists as Neptune is very far from the sun and it was thought that solar energy usually drives atmospheric activity. Having discovered six new moons, Voyager 2 then flew by the last solid body it would encounter in the Solar System, Triton, Neptune’s largest moon and the coldest known object in the Solar System. It orbits in an opposite